1. Field of the Invention
The present invention relates to a device and a method for generating a chaotic signal, which are applied to Ultra Wide Band (hereinafter, referred to as ‘UWB’) communication using an On-Off Keying (OOK) scheme. In the device and the method, a digital-type PN signal generator is used to stably generate a chaotic signal regardless of a process change.
2. Description of the Related Art
In general, the UWB is referred to as a frequency band where a frequency bandwidth occupies more than 25% of a center frequency or is more than 500 MHz.
When the UWB is observed at a time axis, it can be found that the UWB has a very small signal width. Therefore, the UWB can prevent spreading or superposition of signals, caused by multiple propagation paths, and has a strong characteristic with respect to noise interference. Accordingly, the UWB is widely used in location-awareness communication where high-speed communication and precise distance calculation are required.
As for systems which are widely researched as a communication system using the UWB, there is provided a chaos communication system. The chaos communication system uses a chaotic signal having a noise characteristic.
Typically, a square-wave signal has a regular phase in accordance with time. Therefore, when an interference signal with an antiphase is added, the signal can be distorted or offset. However, since a chaotic signal has an aperiodic characteristic like noise, the chaotic signal does not have a clear phase. Accordingly, although an antiphase signal or an approximate interference signal is added, interference does not occur.
Further, since the chaotic signal has an aperiodic characteristic as described above, the chaotic signal has a constant magnitude in a wideband range regardless of a period, when it is analyzed on a frequency axis, which means that the chaotic signal has high energy efficiency.
In addition, the chaos communication system uses an On-Off Keying (OOK) scheme in which a chaotic signal within a microwave band is directly modulated using continuous packet information signals of a modem.
FIG. 1 is a block diagram showing a basic structure of an OOK modulator using a chaotic signal. As shown in FIG. 1, a general OOK modulation scheme is where a chaotic signal is generated to apply a pulse to a Single Pole Double Throw (SPDT) switch. In the OOK modulation scheme, information to be transmitted is divided into information in which a pulse is present (‘1’) and information in which a pulse is not present (‘0’). Further, reception is divided into “1” and “0”, depending on the presence or absence of energy.
As such, the chaos communication system using the OOK scheme, which is a direct modulation scheme, has a few spikes. Therefore, coding such as time hopping or the like is not needed separately in a modem, and circuits such as a phase looked loop (PLL), a mixer, and the like for intermediate-frequency conversion are not needed, which makes it possible to simply implement a transmitting and receiving device.
FIG. 2 is a circuit diagram of a conventional device for generating a chaotic signal. As shown in FIG. 2, the conventional device for generating a chaotic signal includes an oscillator 21, a wideband chaotic signal generator 22, an amplifier 23, and a band-pass filter 24.
In the circuit of FIG. 2, the wideband chaotic signal generator 22 generates a wideband chaotic signal by using a signal generated from the oscillator 21. The amplifier 23 amplifies the generated chaotic signal, and the band-pass filter 24 extracts only a UWB signal in the range of 3.1 to 5.15 GHz.
FIG. 3 is a graph showing a simulation result of FIG. 2, in which a voltage waveform at an output node is converted into a frequency spectrum.
As shown in FIG. 3, it can be found that the conventional device for generating a chaotic signal generates a chaotic signal in the range of 3.1 to 5.5 GHz which corresponds to the UWB.
However, the conventional device for generating a chaotic signal shown in FIG. 2 is sensitive to the value of the passive element A used for generating a chaotic signal and parasitic components existing in a collector and an emitter of the transistor used as the oscillator 21. Therefore, the device has difficulties in generating a stable chaotic signal.
That is, when the value of the passive element A shown in FIG. 2 changes to some degree in accordance with a process change, a chaotic signal may not be generated. FIGS. 4A to 4C are graph for explaining this, showing simulation results when the value of the passive element shown in FIG. 2 changes in accordance with a process change.
FIG. 4A shows a simulation result when a resistor R of the passive element A shown in FIG. 2 changes by 10% in accordance with a process change. FIG. 4B shows a simulation result when an inductor L of the passive element A shown in FIG. 2 changes by 10% in accordance with a process change. FIG. 4C shows a simulation result when a capacitor C of the passive element A shown in FIG. 2 changes by 10% in accordance with a process change.
As shown in FIGS. 4A to 4C, when the value of the passive element A changes to some degree in accordance with a process change, the conventional device for generating a chaotic signal may not generate a chaotic signal in the range of 3.1 to 5.15 GHz. Accordingly, a chaotic signal cannot be stably generated, which means that the device is sensitive to a process change.